RAID (Redundant Array of Independent Disks) is a storage virtualization technique that combines multiple physical drives into a single logical unit. By distributing data across disks, RAID can improve performance, increase usable capacity, and—most importantly—provide protection against disk failures.
🎯 Core Goals of RAID #
RAID designs always balance three competing objectives:
- Performance: Parallel I/O across multiple disks improves throughput and lowers latency.
- Capacity: Multiple disks are aggregated into one logical volume.
- Reliability: Redundancy mechanisms such as mirroring or parity protect against hardware failure.
No RAID level maximizes all three at once; every configuration is a trade-off.
⚡ Standard RAID Levels #
RAID 0 — Striping (Performance Only) #
Data is split into blocks and written across all disks in parallel. This delivers excellent performance but no fault tolerance.
- Fault tolerance: None
- Failure impact: One disk failure destroys the entire array
- Best for: Scratch disks, temporary workloads, video editing caches, benchmarks
RAID 0 should never be used for irreplaceable data.
RAID 1 — Mirroring (Redundancy) #
Each disk contains a complete copy of the data. Reads can be faster, but writes go to all mirrors.
- Fault tolerance: One disk per mirror set
- Usable capacity: 50%
- Best for: OS volumes, small but critical datasets
RAID 1 is simple, robust, and easy to recover.
RAID 5 — Distributed Parity #
Data and parity information are striped across all disks. If one disk fails, data can be reconstructed from parity.
- Minimum disks: 3
- Fault tolerance: 1 disk
- Usable capacity: (N − 1) disks
- Best for: File servers, general-purpose enterprise storage
RAID 5 offers good capacity efficiency but suffers during rebuilds.
RAID 6 — Dual Distributed Parity #
An extension of RAID 5 with two independent parity blocks, allowing two disks to fail simultaneously.
- Minimum disks: 4
- Fault tolerance: 2 disks
- Usable capacity: (N − 2) disks
- Best for: Large arrays with high-capacity drives
RAID 6 significantly improves safety at the cost of write performance.
🔗 Nested (Hybrid) RAID Levels #
RAID 10 (1+0) — Performance + Redundancy #
RAID 10 mirrors disks first, then stripes across mirror pairs. It combines RAID 1 reliability with RAID 0 performance.
- Fault tolerance: One disk per mirror pair
- Usable capacity: 50%
- Performance: Excellent (especially random I/O)
- Best for: Databases, virtualization platforms, latency-sensitive workloads
RAID 10 is often considered the gold standard for performance-critical systems.
📈 2025 Reality: RAID vs. Erasure Coding #
As disk capacities exceed 20–30TB, traditional RAID faces new challenges:
- Long rebuild times: Reconstructing a failed RAID 5/6 disk can take days.
- Increased risk: During rebuilds, remaining disks are under heavy load and more likely to fail.
- Scaling limits: RAID operates within a single server or enclosure.
Modern hyperscale environments increasingly use erasure coding in software-defined storage (SDS) systems. Unlike RAID, erasure coding spreads data across multiple nodes, improving resilience at scale—though often with higher latency.
📊 Quick Comparison #
| RAID Level | Min Disks | Fault Tolerance | Usable Capacity | Performance |
|---|---|---|---|---|
| RAID 0 | 2 | 0 | 100% | Excellent |
| RAID 1 | 2 | 1 | 50% | Good (reads) |
| RAID 5 | 3 | 1 | N − 1 | Balanced |
| RAID 6 | 4 | 2 | N − 2 | Balanced |
| RAID 10 | 4 | 1 per mirror | 50% | Superior |
✅ Conclusion #
RAID is a compromise between cost, performance, and risk.
- For low-risk, high-speed workloads: RAID 0
- For simple, reliable storage: RAID 1
- For balanced enterprise storage: RAID 6
- For performance-critical systems: RAID 10
Even in 2025, RAID remains a foundational technology—especially for single-node systems—while large-scale infrastructures increasingly pair it with software-defined and erasure-coded storage solutions.